Airships of this type are referred to as rigid airships in contrast to so-called nonrigid or pressure airships. The pressure airships have only a single carrier gas cell and do not require a carrier frame. Advances made in the aircraft construction lead to the transport of passengers and goods primarily by aircraft in recent decades. However, there are special fields where the high transport speed of aircrafts is not especially important so that airships could be advantageously used in these special fields. It is, for example, advantageous when an aircraft is capable of cruising for prolonged periods of time in the vicinity of its destination at very low speeds, or even better, if it is capable to remain in a floating or rather, hovering, state for a longer period of time in a fixed location. Incidentally, in this context the term "aircraft" is intended to include airships. Airships are well capable of satisfying these requirements. Thus, repeated investigations have been made with regard to the use of airships. In actual practice, frequently the above mentioned pressure airships, also known as blimps, have been used. These blimps are somewhat smaller in volume and less expensive than conventional rigid airships. Due to avoiding a carrier frame, the blimps are not only lighter, but correspondingly less complicated in their construction and hence less expensive in their manufacture. Another advantage of blimps is the fact that even if they are relatively small, they still can carry a satisfactory payload. However, it is a disadvantage of blimps that their travel speed is rather low due to their plump shape. Another disadvantage is seen in that blimps are not very stable on their course and there is always the problem of gas leakage. When a blimp loses pressure, it is no longer effectively steerable.
Conventional rigid airships normally comprise a carrier frame made of a substantial number of ring-type cross ribs interconnected at junction points by a plurality of longitudinal beams. The ring-type cross-ribs are constructed as polygons comprising, for example, more than twenty cross-rib sections, whereby for satisfying strength requirements each corner of such a polygonal rib is connected with each other corner of the same ring-type rib by tension wires. At the corners of the ring-type ribs junction points are provided for the connection of the mentioned longitudinal beams. These junction points constitute the connection between any given ring to its neighboring rings. The so constructed multi-cornered sections of the carrier frame support the gas cells within the framework. The outer surface of the framework is closed by the so-called outer skin. The lift producing gas cells are held in place inside the framework by netting so that the lift gas cells bear against the inner surfaces of the frame members, whereby an intermediate space is formed between the skin of the individual gas cells and the outer skin of the airship. The frame members are arranged in this intermediate spacing which is lost for producing lift.
The individual cross rib sections of the rib rings and the longitudinal beams are conventionally constructed as a truss or framework. Such a construction involves a substantial technical effort and expense for the formation of the carrier frame. Another disadvantage of a truss-type carrier frame is seen in that it is sensitive against localized force introduction and against vibrations. Thus, even minor accidents may lead to substantial damage of the carrier frame structure which in turn entails a substantial effort and expense for maintenance and repair work. It should also be mentioned in this context that due to the weight of the carrier frame only relatively large rigid airships having a lift volume of several ten thousandths cubic meters, provide a satisfactory payload. However, airships of such sizes are not desirable for many purposes.
The above mentioned drawbacks of rigid airships must be contrasted to a few advantageous characteristics of such rigid airships. For example, due to the aerodynamically advantageous outer contour of rigid airships, they have a higher operational speed and a good course stability as compared to blimps. Another important advantage of rigid airships is their larger safety due to the use of a plurality of gas cells and due to the fact that gas loss is usually limited to one or only a few gas cells. Further, the rigid airship retains its contour and hence remains completely steerable.
A report entitled: "Flight Systems Lighter Than Air", published in March 1976 by the DGLR-Committe 2A6 contains a section entitled: Comparative Structural Investigations of Airship Models, by the "institute for Static and Dynamic Air-and Spacecraft Constructions" of the University of Stuttgart, Federal Republic of Germany. The committee investigates the construction of a carrier frame for airships. The suggestion made in these investigations differentiaties itself from previous rigid airship constructions in that substantially all cross-components of the structure have been obviated. The cross-components have been replaced by a pretensioned, compression loaded outer skin. This type of construction as proposed by said committee provides sustantial weight savings as compared to previous rigid airships while permitting the same structural loading of the carrier frame. The omission of heavy cross-ribs also substantially simplifies the manufacturating operations.
The report refers to carrier frame structures that have been investigated in which instead of the cross-ribs, three beams are provided in the shape of a triangle standing on its tip. The outer skin of the airship is wrapped externally around the three carriers. Longitudinal carrier beam structures are connected to the corners of the three cross carriers. The longitudinal carrier beam constructions interconnect the cross-carrier ribs with each other in sections and sequentially. However, the longitudinal carrier members secured to the lower tip of the triangle are sensitive to damage. Structural details regarding the carrier gas cells and any other structural features of the airship are not provided in said report. The report merely shows that by a simplified triangular construction of the ribs of the carrier frame weight savings are possible.